1. Field of the Invention
The present invention generally relates to a relay communication system. More particularly, the present invention relates to a relay system and method for providing a pilot sequence that optimizes channel estimation performance in a relay communication system.
2. Description of the Related Art
Signal transmission and reception typically take place via a direction link between a Base Station (BS) and a Mobile Station (MS) in a communication system. Relative to the fixedness of BSs, however, a wireless network is not flexibly configured, shadowing area exists, and provisioning of an efficient communication service is difficult in a radio environment experiencing fluctuating change in channel status. To overcome these shortcomings, Relay Stations (RSs) are introduced.
A relay communication system increases system capacity and expands cell coverage. When the channel status between a BS and an MS is poor, an RS is positioned between them, thereby providing a better radio channel to the MS via an RS-based relay link. Signal relaying enables an MS at a cell boundary having a poor channel status to use a higher-rate data channel and expands cell coverage. The configuration of the a conventional relay communication system will be described with reference to FIG. 1.
FIG. 1 illustrates the configuration of a conventional relay communication system.
Referring to FIG. 1, the relay communication system includes, for example, a BS 111, an RS 113 and an MS 115. The RS 113 provides a relay path between the BS 111 and the MS 115.
Although the MS 115 and the BS 111 can communicate with each other by direct signal transmission and reception, it is assumed herein that the MS 115 communicates with the BS 111 with the aid of the RS 113. The RS 113 relays signals between the BS 111 and the MS 115 in a Decode-and-Forward (DF) strategy, and the MS 115 exchanges signals with the BS 111 via the RS 113.
Let a channel between the BS 111 and the RS 113 be denoted by hBR, a channel between the RS 113 and the MS 115 be denoted by hRM, and a channel between the BS 111 and the MS 115 be denoted by hBM. If the BS 111 transmits a signal xB, a signal received at the RS 113 and a signal to be forwarded by the RS 113 are given as Equation (1);yR=hBRxB+nRxR={circumflex over (x)}B  (1)where yR denotes the signal received at the RS 113 from the BS 111, nR denotes noise received at the RS 113, and {circumflex over (x)}B denotes an estimate of xB detected by the RS 113.
Meanwhile, the MS 115 receives the signal from the BS 111 via the RS 113. The received signal is expressed as Equation (2);yM=hRM{circumflex over (x)}B+nM  (2)where yM denotes the signal received at the MS 115 from the BS 111 via the RS 113 and nM denotes noise received at the MS 115.
The communication system uses a DF half duplex relay scheme. For one time period, one transmitter, for example, one of the BS 111 and the RS 113 transmits a signal. With reference to FIG. 2, the DF half duplex relay scheme will be described below.
FIG. 2 illustrates a conventional half duplex relay scheme.
Referring to FIG. 2, an RS relays a signal received from a BS to an MS in a relay communication system. Two time periods, T1 and T2 are defined for signal transmission/reception.
At T1, the BS transmits a signal ‘x1’ and the RS receives the signal ‘x1’ without any signal transmission. At T2, the BS discontinues signal transmission and the RS decodes and forwards the received signal ‘x1’ to the MS. The half duplex relay scheme is characterized in that each transmitter, for example, the BS or the RS transmits a signal during a different time period.
In the half duplex relay communication system, only one transmitter operates during one time period, even if two or more transmitters have transmission data during the time period. Therefore, system capacity is not efficiently utilized.